Kinda strange this wasn't ever answered. If you want to use the npm version with custom less, then this is probably the most straight forward way.

Install as npm install font-awesome --save-dev

In your development less file, you can either import the whole font awesome less using @import "node_modules/font-awesome/less/font-awesome.less", or look in that file and import just the components that you need. I think this is the minimum for basic icons: